The present invention relates to an anti-bounce device for preventing the multiple shocks of a moving mass after a first shock or impact against another element.
The device of the invention may be used for very different applications. It finds its application more particularly in the field of seismic or acoustic wave sources where a moving mass forcibly strikes a target element against which it is precipitated by gravity and/or drive means. A percussion source for land seismic prospection comprising a mass falling along a guide means towards a target element anchored against the surface of the ground is described in French Pat. No. 2 398 316 and corresponding U.S. Pat. No. 4,205,731. Another, adapted more particularly to use in a borehole, is described in French Pat. No. 2 552 553. The use of drive means for hurling a mass against a target element anchored in a well described in French Pat. No. 2 558 and corresponding U.S. Pat. No. 4,648,478.
When the mass is left free, it generally bounces after impact against the associated target element and then strikes it one of more times with decreasing force. The "signature" of the seismic source, i.e. the shape of the pulses which it emits, comprises then in this case several secondary pulses of decreasing amplitude following the main pulse and this disturbs the seismic recordings corresponding to the seismic reflections from the discontinuities of the sub-soil of the shocks transmitted.
In French Pat. Nos. 1 337 935 and 548313 sound generators are described comprising members vibrating under the effect of the shocks of striking elements hurled towards them, and means for exerting recoil forces which prevent said striking elements from again coming into contact after the first impact.
From the French Pat. No. 2,509,052, and corresponding U.S. Pat. No. 4,505,362 a device is known or preventing multiple shocks on a target element, coupled with the surface of the ground, of a mass guided in its fall by guide means, with these multiple shocks being due to bouncing of the mass after its first impact. This device comprises essentially a deformable element fastened to the guide means and control means adapted for applying the deformable element against the lateral wall of the mass after its first bounce and immobilizing it before it falls again. The control means comprise, for example, a movable member moved radially by the action of a hydraulic cylinder and an impact detector delivering a cylinder control signal.
This device very efficiently stops any falling back of the mass but, because of its transverse position perpendicular to the longitudinal axis of the guide means, its size would not be compatible with the reduced dimensions of boreholes in which the well seismic sources are generally lowered.